1. Field of the Invention
This invention relates to liquid crystal light valve systems, and more particularly concerns improvement in optical rise time of such a system.
2. Description of Related Art
The liquid crystal light valve (LCLV) is a thin film multi-layer structure comprising a liquid crystal layer between a pair of alignment layers, a dielectric mirror layer, a light blocking layer and a photosensitive layer, all sandwiched between two transparent electrodes. In a typical reflective LCLV projection system, a high intensity polarized projection beam is directed through the liquid crystal layer to the dielectric mirror. An input image of low intensity light, such as that generated by a cathode ray tube, is applied to the photosensitive layer, thereby switching the electric field across the electrodes from the photosensitive layer onto the liquid crystal layer, so as to selectively activate the liquid crystal according to the intensity of input light received at different areas of the photosensitive layer. Linearly polarized projection light from a light source (often, but not always of high power), such as a Xenon lamp, passes through the liquid crystal layer and is reflected from the dielectric mirror. The light is polarization modulated going into and coming from the system. It is reflected from the mirror and polarization modulated by the liquid crystal in accordance with light information incident on the photo responsive layer. Therefore, if a complex spatial distribution of light, for example a high resolution input image from a cathode ray tube, is focused onto the photosensitive layer, the liquid crystal layer light valve converts the low intensity input image into a replica image which can be reflected for projection with magnification to produce a high brightness image on a viewing screen. Projection systems of this type are described in several U.S. patents, including U.S. Pat. Nos. 4,650,286 to Koda, et al for Liquid Crystal Light Valve color Projector; 4,343,535 to Bleha, Jr. for Liquid Crystal Light Valve; 4,127,322 to Jacobson, et al for High Brightness Full Color Image Light Valve Projection System; and 4,191,456 to Hong, et al for Optical Block For High Brightness Full Color Video Projection System.
The ability of such a projection system to respond to fast variations of input light depends in large part upon the speed of optical response of the liquid crystal material.
Accordingly, it is an object of the present invention to provide a liquid crystal light valve having improved optical response time.